I think most private dentists charge about £20/$25 for a radiography in the UK. In the US, this pricing seems also available -
https://www.teethtalkgirl.com/dental-health/cost-for-dental-....
Interestingly, I lived in Central Europe for a while and all my private dentists just used visual inspection for teeth. I never had an issue with that, all decay was spotted in time and in many cases earlier than with the x-ray only method, because more attention was paid to how the teeth look up-close, at all angles.
However, the visual inspection takes more time and skill. One might argue x-ray is the cheaper and quicker option. Though it costs more to the patient in many cases. Ah, the world of dentistry.